Method for operating a charge conserving driver circuit for capacitive loads

ABSTRACT

A CMOS driver device including an output stage having a first PMOS transistor and an NMOS transistor serially connected between a first voltage and ground and having a second PMOS transistor and the NMOS transistor serially connected between the second voltage and ground. The driver device further includes control logic for mutually exclusively controlling the first PMOS transistor and the second PMOS transistor such that during a first time period an output of the output stage is driven to the first voltage and that during a second subsequent time period the output is driven to the second voltage. The control logic further includes logic for mutually exclusively controlling the first and second PMOS transistors and the NMOS transistor such that prior to enabling one of the first and second PMOS transistors, the NMOS transistor is disabled.

This application is a continuation of U.S. patent application Ser. No.08/495,889, filed on Jun. 28, 1995, now U.S. Pat. No. 5,627,487.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to integrated circuits. Inparticular, the present invention relates to charge conserving,bi-parallel, low to high voltage CMOS driver circuits for drivingcapacitive loads.

BACKGROUND OF THE INVENTION

Dynamic integrated circuit memories such as a dynamic random accessmemory (DRAM) traditionally store data as a charge on a memory cellcapacitor. For example, a logical "one" is stored as positive charge onthe capacitor and a logical "zero" is stored as negative charge on thecapacitor. Because of the dense population of memory cells in anintegrated circuit, the capacitance of each memory cell is small and theavailable charge is proportionally small. To read data from the memorycells, therefore, the charge must be sensed and amplified.

Typical memory circuits are designed to have pairs of data linesselectively coupled to the memory cells. The data line pairs arepre-charged to an equal potential between ground and the supplypotential. When a memory cell is coupled to one of the data lines, adifferential voltage is established between the data line pairs. Ann-channel sense amplifier is used to detect the differential voltage andpull the low data line to ground. Likewise, a p-channel sense amplifieris used to detect the differential and drive the high data line to thesupply voltage.

As stated, the DRAM memory cell is dynamic, and as such the data must beperiodically refreshed by writing back the data to the memory cell. Toextend the period between write backs, the initial charge stored on thememory cell should be provided using the maximum available potentialvoltage. To maintain a maximum charging potential during the memory cellrefresh, the p-sense amplifiers may be coupled directly to the memorycell, or by using an isolation device, such as a transistor having apumped gate voltage. Additional current must, therefore, be provided tosource the pumped gate voltage.

Driver circuits for driving devices such as the isolation device whichrequires a pumped gate voltage have typically pulled all the chargenecessary to drive the load from a pumped or elevated voltage source.Such drivers require an undesired level of current needed to drive theisolation devices entirely from the pumped voltage source.

In addition, conventional output driver circuits utilize complementarymetal-on-semiconductor (CMOS) technology. A conventional CMOS outputcircuit includes a p-channel MOS (PMOS) transistor coupled betweenvoltage and an output node, and an n-channel MOS (NMOS) transistorcoupled between the output node and ground. The CMOS design enables thePMOS transistor to be "on" while the NMOS transistor is "off", and viceversa, in response to a single input signal. When the PMOS transistor is"on" and the NMOS transistor is "off", the CMOS driver circuit outputs avoltage. Conversely, when the PMOS transistor is "off" and the NMOStransistor is "on" , the output of the CMOS driver circuit is grounded.

A drawback inherent in the design of conventional CMOS output drivercircuits is that during the low to high voltage swing at the input tothe device, there exists a period of time when both the PMOS and NMOStransistors are "on." This dual activation condition causes a phenomenonknown as "crossing current" which wastes power.

Therefore, there is a need in the art for a driver circuit that reducesthe level of charge pulled from the pumped or elevated voltage source.In addition, the driver circuit should eliminate or substantially reducecrossing current in an effort to conserve power.

SUMMARY OF THE INVENTION

The above mentioned problems and others are addressed by the CMOS driverdevice of the present invention. The CMOS driver device includes acontrollable CMOS output stage for providing a translated output signalbased on one of a first and a second level input signal. The drivercircuit further includes output stage control logic for receiving one ofthe first and the second level input signal. The output stage controllogic includes first and second parallel voltage translators to generatecontrol signals for controlling the controllable CMOS output stage anddelay logic to control the first and second parallel voltagetranslators. The first and second parallel voltage translators arecontrolled such that a translated output signal representative of theone of the first and the second level input signal is derived in partfrom one of a first and second voltages during a first time period andin part from the other of the first and second voltages during asubsequent second time period.

In another embodiment, the delay logic includes input delay logic forreceiving the one of the first and the second level input signal. Theinput delay logic activates the first voltage translator such that thetranslated output signal representative of the one of the first and thesecond level input signal is derived in part only from the first voltageduring the first time period and subsequently deactivates the firstvoltage translator and activates the second voltage translator such thatthe translated output signal representative of the one of the first andthe second level input signal is derived in part only from the secondvoltage during the subsequent second time period.

In another embodiment, the output stage control logic includestranslator output logic. The translator logic receives translator outputsignals from each of the first and second voltage translators such thatthe controllable CMOS output stage is activated such that a transitionbetween a first level output signal and a second level output signal isperformed in a time staggered manner to minimize crossing current in thecontrollable CMOS output stage when the input signal transitions betweenfirst and second levels.

In another embodiment, the CMOS driver device includes an output stagehaving a first PMOS transistor and an NMOS transistor serially connectedbetween a first voltage and ground and having a second PMOS transistorand the NMOS transistor serially connected between the second voltageand ground. The driver device further includes control logic formutually exclusively controlling the first PMOS transistor and thesecond PMOS transistor such that during a first time period an output ofthe output stage is driven to the first voltage and that during a secondsubsequent time period the output is driven to the second voltage. Thecontrol logic further includes logic for mutually exclusivelycontrolling the first and second PMOS transistors and the NMOStransistor such that prior to enabling one of the first and second PMOStransistors, the NMOS transistor is disabled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a low to high CMOS driver circuit inaccordance with the present invention;

FIG. 2 is a schematic drawing of the low to high CMOS driver circuitshown in FIG. 1;

FIG. 3 is a diagram showing the output signal provided at the output ofthe output stage of the driver circuit of FIG. 2 and various controlsignals for control of the output stage of the driver circuit of FIG. 2;

FIG. 4 is a diagram showing the signals shown in FIG. 3 superimposedupon one another during a low to high transition of the input signal ofthe driver circuit of FIG. 2;

FIG. 5 is a diagram showing the signals shown in FIG. 3 superimposedupon one another during a high to low transition of the input signal ofthe driver circuit of FIG. 2;

FIG. 6 is a diagram showing the charging current for the diagram shownin FIG. 3; and

FIG. 7 is a schematic diagram for an alternate embodiment of the voltagetranslator of the driver circuit shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiment,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical and electricalchanges may be made without departing from the scope of the presentinventions. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present inventions isdefined by the appended claims.

Each transistor described herein is either a P-channel or N-channelfield-effect transistor (FET) having a gate, a first current node(drain) and a second current node (source). Since a FET is typically asymmetrical device, the true designation of "source" and "drain" is onlypossible once a voltage is impressed o the terminals. The designationsof source and drain herein should be interpreted, therefore, in thebroadest sense.

The low to high voltage CMOS driver circuit 10, in accordance with thepresent invention shall be generally described with reference to FIG. 1and FIG. 3. The driver circuit 10 includes an output stage 14 forproviding an output signal 15 under control of output stage controllogic 12 and indicative of the input voltage applied on input 11. Theoutput stage 14 includes an NMOS transistor 74 and a PMOS transistor 70coupled between a first voltage level Vcc and another voltage level,such as ground. The output stage further includes another PMOStransistor 72 coupled with the NMOS transistor 74 between a secondvoltage source, such as a pumped voltage source Vccp, and ground. TheCMOS output stage 14 provides an output signal 15 that swings betweenthe first and second voltage levels and ground depending upon whetherthe NMOS transistor 74 and PMOS transistors 70, 72 are driven "on" or"off" by control signals 97-99.

The CMOS driver circuit 10 is designed to drive a capacitive load. Oneexample capacitive load is an isolation device used in memory arraysdriven by an elevated voltage such as Vccp. Such a driver circuit mayalso be beneficial for driving a global row select line in asemiconductor memory array or other devices being driven at a pumped orelevated voltage. CMOS driver circuit 10 translates a low voltage inputsignal 11, such as an isolation device signal ISO (FIG. 2), which swingsbetween Vcc (e.g., 2.5 volts) and ground to a high voltage output signal15, such as isolation device signal ISO* (FIG. 2), which swings betweenVccp (e.g., 4.0 volts) and ground. The notation ISO* denotes a voltagetranslated version of the input signal ISO. The notation "Vccp" iscustomary to denote a higher voltage or pumped-up level above Vcc.

The output stage control logic 12 of the CMOS driver circuit 10 includesmeans for controlling the output stage 14 via control signals 97-99 as afunction of the received input signal 11 indicative of a desired outputsignal 15. The output stage control logic 15 generates independentcontrol signals 97-99 which are used to selectively enable and disablethe transistors in the CMOS output stage 14. That is, independentcontrol signal 97 is coupled to turn "on" and "off" the NMOS transistor,independent control signal 98 is coupled to turn "on" and "off" the PMOStransistor 72 connected to Vccp, and independent control signal 99 iscoupled to turn "on" and "off" the PMOS transistor 70 connected to Vcc.Output stage control logic 12 provides control of output stage 14 suchthat PMOS transistors 70, 72 are operated in a mutually exclusivefashion; therefore, only one of these devices is "on" at any given time.

The output stage control logic 12 includes a pair of voltage translatorstages 18 and 20, input delay logic 22, and translator output logic 74.The first voltage translator 18 drives the PMOS transistor 70 and thesecond voltage translator 20 drives PMOS transistor 72. Both the firstvoltage translator 18 and the second voltage translator 20 providetranslator output control signals 95, 96 to translator output logic 24to generate control signal 97 for enabling and disabling NMOS transistor74.

When input signal 11 transitions from low to high, the input delay logicapplies an internal signal 90 representative of the low to hightransition to the first voltage translation stage 18, but not the secondvoltage translation stage 20. The first translator stage 18 generatescontrols signals 95 and 99 for disabling NMOS transistor 74 viatranslator output logic 24 and enabling PMOS transistor 70, which drivesthe output signal 15 to Vcc. The input signal 11 is delayed by inputdelay logic 22 prior to an internal signal 91 representative of the lowto high transition being applied to the second voltage translation stage20 and internal input signal 90 is altered such that the first voltagetranslation stage turns off PMOS transistor 70. The second voltagetranslation stage 20 then generates control signals 96 and 98 forturning on PMOS transistor 72 and maintaining the disabled state of NMOStransistor 74. The output signal 15 is then driven to Vccp. Therefore,the output stage 14 is controlled such that the PMOS transistors 70, 72are operated in a mutually exclusive fashion and as shown in FIG. 3, theoutput signal 15 is brought to about Vcc via PMOS transistor 70 and thento about Vccp via PMOS transistor 72. Control signals 97-99 are alsogenerated such that when the input signal is transitioned low or toground, the output signal 15 also is brought to ground.

Further, the output stage control logic 12 generates control signals97-99 such that the NMOS transistor 74 is turned "off" before turning"on" the disabled PMOS transistor 70. In this manner, the output stagecontrol logic 12 independently activates the NMOS transistor 74 and PMOStransistors 70, 72 in a time-staggered manner to minimize crossingcurrent in the CMOS output stage during transitions of the input signal11. This saves power which would otherwise be lost due to crossingcurrent. This independent activation is best shown in FIG. 4 wherein thecontrol signal 97 transitions low prior to control signal 99 and in FIG.5 wherein the control signal 98 transitions high prior to the controlsignal 97.

The present invention shall now be described in further detail withreference to FIGS. 2-6. The low to high voltage CMOS driver 10 inaccordance with the present invention, includes output stage 14, inputdelay logic 22, parallel voltage translations stages 18, 20, andtranslator output logic 24. The CMOS output stage 14 includes the NMOStransistor 74 which has a source-to-drain path coupled between driveroutput 15 and ground or a first voltage level. The CMOS output stage 14also has a first PMOS transistor 70 and a second PMOS transistor 72. Thefirst PMOS transistor 70 has a source-to-drain path coupled between asecond voltage level, or Vcc, and driver output 15 and second PMOStransistor 72 has a source-to-drain path coupled between a third voltagelevel, or Vccp, and driver output 15. The third voltage level is apumped or elevated voltage level with respect to the Vcc and may begenerated therefrom utilizing additional circuitry as is known to oneskilled in the art.

The PMOS transistors 70, 72 and the NMOS transistor 74 in the CMOSoutput stage 14 are controlled by three independent control signals97-99. When the PMOS transistor 70 is "on" and the NMOS transistor 74 is"off," the output signal 15 is at Vcc. When PMOS transistor 72 is "on"and the NMOS transistor 74 is "off," the output signal 15 is at Vccp.Further, when the PMOS transistors 70, 72 are "off" and the NMOStransistor 74 is "on," the output signal 15 is at ground. In thisembodiment, the input signal 11 is ISO and the output signal 15 is ISO*for driving an isolation device as generally described previously. Thespecification of such input and output is only for illustrative purposesonly is not to be taken as limiting the claims of the present inventionin any manner. Various inputs and outputs are contemplated in accordancewith the present invention, such as the global row select previouslymentioned.

Input delay logic 22 includes delay element 32, inverter 30 and NOR gate34. Both the delay element 32 and the inverter 30 are coupled to receivethe input signal 11. The inverter 30 is connected to provide its outputto one of the inputs of the NOR gate 34 and the other input of the NORgate 34 is coupled to the output of the delay element 32. The output 90of the NOR gate 34 is applied to the first voltage translation stage 18and the output 91 of the delay element 32 is applied to the secondvoltage translation stage 20.

The components of input delay logic 22 including delay element 32 areselected such that when the input signal 11 transitions high, thetransitioned input signal or output 90 representative of thetransitioned input is provided to the first voltage translation stage18. The delay element 32 delays the application of the transitionedinput signal or output 91 from being applied to the second voltagetranslation stage 20 such that output signal 15 is driven to Vcc duringa time period substantially equal to the delay period. Then the delayedinput signal 91 is applied to the NOR gate 34 to provide an output 90that results in the gate of PMOS transistor 70 being driven to Vccp and,therefore "off." The delayed signal 91 is also applied to the secondvoltage translation stage 20 such that PMOS transistor 72 is turned "on"with the output signal 15 being driven to Vccp. Therefore, the inputdelay logic 22 controls the first and second voltage translation stages18, 20 in a mutually exclusive fashion such that PMOS transistors 70, 72are driven independently. In one particular embodiment, such mutuallyexclusive operation allows for about half the charge required for theload on output 15 to come from Vcc and about half from Vccp. Thisdelayed operation is shown in the diagrams of FIGS. 3-6 as describedfurther below.

The output signals 90, 91 of the input delay logic 22 are each appliedto one of the first and second voltage translation stages 18, 20. Thefirst voltage translation stage 18 which receives the output 90includes: inverters 40, 41; a NOR latch including NOR gates 43, 44; andtransistors 42, 45-49. The second voltage translation stage 20 is likethat of the first and includes: inverters 50, 51; a NOR latch includingNOR gates 52, 53; and transistors 54-59. Each operate in the same manneras described below and each generates two control signals. The firstvoltage translation stage 18 provides control signals 95, 99 and thesecond voltage translation stage 20 provides control signals 96, 98. Thefirst and second voltage translation stages 18 and 20 in conjunctionwith the translator output logic 24 provide for the elimination of orminimization of crossing current in the output stage 14 as describedbelow.

The translator output logic 24 of the output stage control logic 12includes a NAND gate 65 and an inverter 66. The NAND gate 65 receivesthe translator output signals 95, 96 from the first and second voltagetranslation stages and the inverter is coupled to the output of the NANDgate 65 and to the gate of NMOS transistor 74 for control thereof.

The inverters 40, 41 and the NOR latch 39 of the first voltagetranslation stage 18 form an input stage 38 thereof for receiving theoutput 90 of input delay logic 22. Input stage 38 generates threeindependent control signals 92, 93, and 95 based upon the output signal90 of the input delay logic 22. The control signal 95 is provided to oneof the inputs of NAND gate 65 of the translator output logic 24 with thetranslator output signal 96 from the second translation stage 20. Theoutput of the NAND gate 65 is then inverted and applied as controlsignal 97 to NMOS transistor 74 to control the gate thereof, and therebyactivate or deactivate the NMOS transistor 74. The other two signals 92,93 are input to voltage translation portion 37 of the first voltagetranslation stage 18, as described below in more detail.

Input stage 38 includes latch 39 which generates the control signals 93,95. Latch 39 is preferably configured as a cross-coupled NOR gate latchhaving NOR gates 43 and 44. Input stage 38 also includes the inverter 40to initially invert signal 90 and the other inverter 41 is coupledbetween the first inverter and the input of NOR gate 44.

The voltage translation portion 37 of the first voltage translationstage 18 is coupled between input stage 38 and output stage 14. Thevoltage translation portion 37 receives the internal control signals 92and 93 from the input stage 38, and uses these control signals 92, 93 togenerate an independent, higher voltage activation control signal 99.This control signal 99 is utilized to control the PMOS transistor 70 ofoutput stage 14. Due to the inherent delay time that it takes signal 90to propagate through input stage 38 and voltage translation portion 37,the control signal 99 is time staggered from control signal 95. As aresult, control signal 97 generated as a function of control signal 95and control signal 99 independently turn "on" and "off" the PMOStransistor 70 and NMOS transistor 74. This independent control minimizesor eliminates crossing current in the CMOS output stage 14.

Voltage translation portion 37 includes a pair of cross-coupled PMOStransistors 47 and 49. The PMOS transistor 47 has a source-to-drain pathcoupled between Vccp and a first node 36. The PMOS transistor 49 has asource-to-drain path coupled between Vccp and an output node 35 which iscoupled to the gate of PMOS transistor 70 in output stage 14. The gateof the PMOS transistor 49 is coupled to node 36 and the gate of the PMOStransistor 47 is coupled to output node 35 to form the cross-coupledPMOS transistor structure.

Voltage translation portion 37 further includes a first NMOS controltransistor 42 which has a source-to-drain path coupled between node 36and ground. The gate of control transistor 42 is coupled to receive theinternal control signal 92 from input stage 38. A second NMOS controltransistor 48 has a source-to-drain path coupled between output node 35and ground. The gate of this second control transistor 48 is coupled toreceive the internal control signal 93 from input stage 38.

Control transistors 42 and 48 control the pair of cross-coupled PMOStransistors 47 and 49 to alternately output at output node 35 a controlsignal 99 that swings between Vccp and ground. Internal signals 92 and93 selectively turn "on" and "off" control transistors 42 and 48 in analternating, out-of-phase fashion. When control transistor 42 is "on"and control transistor 48 is "off," first node 36 is grounded, therebyturning "on" PMOS transistor 49. The Vccp voltage is thus placed atoutput node 35, keeping PMOS transistor 47 in an "off" state. Whencontrol transistor 48 is "on" and control transistor 42 is "off", outputnode 35 is grounded and PMOS transistor 47 is turned "on." The otherPMOS transistor 49 is then turned "off" and the voltage translationportion 37 outputs a ground level voltage at output node 35 as controlsignal 99.

According to another aspect of the driver circuit 10, voltagetranslation portion 37 of the first voltage translation stage 18includes NMOS precharge transistors 45 and 46. The first NMOS prechargetransistor 46 has a gate coupled to the gate of the second NMOS controltransistor 48 and to the input stage 38. Precharge transistor 46 isselectively activated by the internal control signal 93. Prechargetransistor 46 has a source-to-drain path coupled between Vcc and thefirst node 36. Similarly, a second NMOS precharge transistor 45 has agate coupled to the gate of the first NMOS control transistor 42 and toinput stage 38. Precharge transistor 45 is selectively activated by theinternal control signal 92. Precharge transistor 45 has asource-to-drain path coupled between Vcc and output node 35.

The precharge transistors 45 and 46 raise respective nodes 35 and 36toward Vcc before the cross-coupled PMOS transistors 47 and 49 turn "on"to further increase the voltage levels at those nodes to Vccp. Forexample, when internal control signal 93 goes high to turn "on" controltransistor 48, it simultaneously turns "on" precharge transistor 46. Asa result, first node 36 begins to rise from ground towards Vcc-Vt,wherein Vt is the threshold voltage of the transistor. Within a minortime delay, PMOS transistor 47 is turned "on" to further raise thevoltage level at first node 36 to Vccp. The precharge transistor 45 doesessentially the same function for output node 35. These prechargetransistors help reduce Vccp current through the voltage translationportion 37 during a transition.

Precharge transistors 45 and 46 form one implementation of a prechargemeans for precharging the pair of cross-coupled transistors 47 and 49 tofacilitate transition during toggle between the two output states. Othergate arrangements besides the single NMOS transistors shown can also beused to precharge the respective nodes. Example alternate embodimentsmight include PMOS transistors, pass circuits having a combination PMOSand NMOS transistors, or other equivalent structures.

The second voltage translation stage 20 contains substantially the sameelements as the first voltage translation stage and operates insubstantially the same manner. Therefore, a detailed description withregard to the second voltage translation stage 20 shall not be provided.In general, the second voltage translation stage 20 provides controlsignal 98 for control of PMOS transistor 72 of the output stage 14. Itfurther also provides translator output signal 96 to translator outputlogic 22 with the translator output signal 95 from the first voltagetranslation stage for control of NMOS transistor 74 in a time staggeredmanner with respect to activation and deactivation of PMOS transistors70 and 72 via NAND gate 65 and inverter 66.

FIG. 7 illustrates an alternate embodiment for the voltage translationstages 18 and 20 of the driver circuit 10 in accordance with the presentinvention. The alternate voltage translation stage 100 differs frompreviously described voltage translation stages of FIG. 2 in that inputstage 103 includes a cross-coupled NAND gate latch 101 having a firstNAND gate 106 and a second NAND gate 108. Input stage 103 furtherincludes inverters 102 and 104 on the front end of NAND gate latch 101,and inverters 112 and 110 on the back end of the NAND gate latch 101.According to this construction, input stage 103 outputs three controlsignals A, B, and C. This embodiment also reduces crossing current inboth the voltage translation stage 100 and output stage 14.

FIG. 3 illustrates a separated timing diagram of the independent controlsignals 97-99 generated by the output stage control logic 12 used toactivate respective transistors 74, 72, and 70 of output stage 14. Alsoillustrated is the output signal 15. The timing diagram proceeds througha first transition from low to high at the input 11 and then a secondtransition back to low. The transitions of input signal 11 respectivelyprovide a first transition of output signal 15 from ground to Vccp(e.g., 4.0 volts) and a second transition from Vccp back to ground.During the first transition, independent control signal 97 goes low tofirst turn "off" NMOS transistor 74. Subsequently, the secondindependent control signal 99 goes low to turn "on" PMOS transistor 70.Due to the time-staggered nature of these two signals because of thedelay through the input stages and the voltage translation portions ofthe first and second voltage translation stages 18 and 20 as opposed tothe control signals 95 and 96 being applied to translator output logic24 for control of NMOS transistor 74, output stage 14 experiences littleor no crossing current during the transition. Accordingly, the operationconserves power by avoiding the crossing current. The composite diagramof the first transition in FIG. 4 shows the time staggered naturebetween control signal 97 transitioning low and control signal 99transitioning low. As a result, minimal crossing current occurs as shownin FIG. 6 at reference number 200.

During the time control signal 99 is low and PMOS transistor 70 isenabled, the output signal 15 is being driven to Vcc. After the inputsignal 11 has proceeded through delay element 32, the control signal 99from the first voltage translation stage 18 is forced high and thereforePMOS transistor 70 is disabled. Subsequently, the control signal 98transitions low and PMOS transistor 72 is enabled driving the outputsignal 15 to Vccp. As a result of first driving the output with Vcc andthen driving the output with Vccp, the charge removed from Vccp isreduced. This is particularly important since Vccp is a pumped voltagesupply. The current drawn during the output being driven by Vcc and thenVccp is shown in FIG. 6. Icc is the current drawn during the outputbeing driven to Vec and Iccp is the current drawn during the outputbeing driven to Vccp.

During the second transition when input signal 11 transitions to ground,independent control signal 99 does not change states. However, controlsignal 98 returns high to first turn "off" PMOS transistor 72.Subsequently, independent control signal 97 returns high to thereby turn"on" NMOS transistor 74. Again, the time-staggered nature of these twoindependent control signals prevents crossing current during thetransition. This time-staggered effect is shown in the composite diagramof FIG. 5 showing the second transition wherein control signal 98transitions high prior to control signal 97. The output signal 15 thenis brought to ground. FIG. 6 shows at reference number 202 the crossingcurrent for the second transition.

As described above, FIG. 6 shows the load current spikes measured atoutput stage 14 which occur during the first and second transitionsshown in FIGS. 3-5. These load current spikes represent the currentflowing through PMOS transistor 70 and 72 and NMOS transistor 74 into acapacitive load. If no crossing current existed, current spikes 200 and202 would be eliminated.

It is further noted that the CMOS driver circuit 10 minimizes crossingcurrent in the voltage translation stages 18 and 20. Accordingly, thecircuit effectively eliminates or substantially reduces crossing currentin both the output stage 14 and the voltage translation stages 18 and20.

It is to be understood, however, that even though numerouscharacteristics of the present invention have been set forth in theforegoing description, together with details of the structure andfunction of the invention, the disclosure is illustrative and changes inmatters of order, shape, size, and arrangement of the parts, and variousproperties of the operation may be made within the principles of theinvention and to the full extent indicated by the broad general meaningof the terms in which the appended claims are expressed.

What is claimed is:
 1. A method for operating a charge conserving drivercircuit, comprising the steps of:transitioning an input signal from alow level to a high level; creating a first internal signalrepresentative of the input signal; applying the first internal signalto a first voltage translation stage; generating a first control signalin the first voltage translation stage to disable a first transistorwith translator output logic; generating a second control signal in thefirst voltage translation stage to enable a second transistor; alteringthe first internal signal; disabling the second transistor with thefirst voltage translation stage before a second internal signalrepresentative of the input signal is applied to a second voltagetranslation stage; creating the second internal signal; applying thesecond internal signal to the second voltage translation stage;generating a third control signal in the second voltage translationstage to enable a third transistor; and generating a fourth controlsignal in the second voltage translation stage to maintain the disabledstate of the first transistor with translator output logic.
 2. Themethod of claim 1, further comprising the steps of:driving an outputsignal to Vcc after the first and second control signals have beengenerated; and driving the output signal to Vccp after the third andfourth control signals have been generated.
 3. The method of claim 1,further comprising the step of driving an output signal to ground afterthe input signal is transitioned from a high level to a low level.
 4. Amethod for operating a charge conserving driver circuit, comprising thesteps of:transitioning an input signal from a low level to a high level;creating a first internal signal representative of the input signal;applying the first internal signal to a first voltage translation stage;generating a first control signal in the first voltage translation stageto disable a first transistor with translator output logic; generating asecond control signal in the first voltage translation stage to enable asecond transistor, wherein the first transistor is disabled before thesecond transistor is enabled; altering the first internal signal;disabling the second transistor with the first voltage translation stagebefore a second internal signal representative of the input signal isapplied to a second voltage translation stage; creating the secondinternal signal; applying the second internal signal to the secondvoltage translation stage; generating a third control signal in thesecond voltage translation stage to enable a third transistor; andgenerating a fourth control signal in the second voltage translationstage to maintain the disabled state of the first transistor withtranslator output logic.
 5. The method of claim 4, further comprisingthe steps of:driving an output signal to Vcc after the first and secondcontrol signals have been generated; and driving the output signal toVccp after the third and fourth control signals have been generated. 6.The method of claim 4, further comprising the step of driving an outputsignal to ground after the input signal is transitioned from a highlevel to a low level.
 7. A method for operating a charge conservingdriver circuit, comprising the steps of:transitioning an input signalfrom a low level to a high level; creating a first internal signalrepresentative of the input signal; applying the first internal signalto a first voltage translation stage; generating a first control signalin the first voltage translation stage to disable an NMOS transistorwith translator output logic; generating a second control signal in thefirst voltage translation stage to enable a first PMOS transistor,wherein the NMOS transistor is disabled before the first PMOS transistoris enabled; altering the first internal signal; disabling the first PMOStransistor with the first voltage translation stage before a secondinternal signal representative of the input signal is applied to asecond voltage translation stage; creating the second internal signal;applying the second internal signal to the second voltage translationstage; generating a third control signal in the second voltagetranslation stage to enable a second PMOS transistor; generating afourth control signal in the second voltage translation stage tomaintain the disabled state of the NMOS transistor with translatoroutput logic; driving an output signal to Vcc after the first and secondcontrol signals have been generated; driving the output signal to Vccpafter the third and fourth control signals have been generated; drivingthe output signal to ground after the input signal is transitioned froma high level to a low level; wherein the input delay logic isoperatively coupled to the input signal, and first and second voltagetranslation stages; wherein the first voltage translation stage isoperatively coupled to the first PMOS transistor and the translatoroutput logic; wherein the second voltage translation stage isoperatively coupled to the second PMOS transistor and the translatoroutput logic; wherein the first PMOS transistor is operatively coupledto Vcc and the output signal; wherein the second PMOS transistor isoperatively coupled to Vccp and the output signal; and wherein the NMOStransistor is operatively coupled to the first and second PMOStransistors and ground.